The invention relates to a fuel injection system for mixture compressing, externally ignited internal combustion engines employing continuous fuel injection into the induction tube of the engine. The induction tube would typically contain an air flow measuring member as well as an arbitrarily actuatable butterfly valve, disposed in series, and the air flow measuring member is deflected corresponding to the air flow rate and in opposition to a restoring force. The moving air measuring member displaces the movable part of a valve in the fuel supply line which meters out a fuel quantity in proportion to the air flow rate. The restoring force is produced by a pressurized fluid which is supplied by a control pressure circuit and which exerts a constant but changeable pressure on the control slide. The control pressure changes are made by at least one electromagnetic valve which operates in dependence on operational engine parameters and at least one pressure control valve which, in particular, may contain a temperature-sensitive heatable valve element.
Fuel injection systems of this type are designed for automatically producing a favorable fuel-air mixture for all operational conditions of the internal combustion engine in order to provide complete fuel combustion, thereby preventing or greatly reducing the generation of toxic exhaust components while maintaining the highest possible power or the least possible fuel consumption of the internal combustion engine. To achieve complete combustion, the fuel must be metered out very precisely depending on the requirements of each operational state of the internal combustion engine and, further, it must be possible to change the fuel-air ratio in dependence on operational engine parameters such as, for example, rpm, load, temperature and exhaust gas composition.
In known fuel injection systems of this type, the fuel quantity is metered out as nearly proportionally as possible to the air quantity flowing through the induction tube and the ratio of the metered out fuel quantity to the air quantity can be altered by changing the magnitude of the restoring force acting on the air measuring member in dependence on engine parameters and by means of a pressure control valve and an electromagnetic valve. Such fuel injection systems require that the fuel system pressure, as regulated by a system pressure valve, is always maintained at the highest pressure required anywhere within the fuel injection system and hence the fuel supply pump and the pressure lines must be dimensioned correspondingly large.